Injectable calcium phosphate cements and the preparation and use thereof

ABSTRACT

A calcium phosphate cement suitable for use in dental and bone prosthesis is disclosed, which include calcium phosphate particles having a diameter of 0.05 to 100 microns, wherein said calcium phosphate particles on their surfaces have whiskers or fine crystals having a width ranging from 1 to 100 nm and a length ranging from 1 to 1000 nm.

RELATED APPLICATION

This is a continuation application and claims the benefit of priorityunder 35 USC § 120 to U.S. patent application Ser. No. 10/414,582 filedon Apr. 16, 2003, which is a continuation-in-part of U.S. patentapplication Ser. No. 09/615,384, filed Jul. 13, 2000, now abandoned,which is a continuation-in-part of U.S. patent application Ser. No.09/351,912, filed Jul. 14, 1999, now U.S. Pat. No. 6,379,453. Thedisclosure of the prior application is considered part of and isincorporated by reference in the disclosure of this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a calcium phosphate cement, and inparticular a fast-setting calcium phosphate cement, for use in dentaland bone prosthesis.

2. Description of the Related Art

A calcium phosphate cement (abbreviated as CPC) has been widely used asan implant or filling material in dental and bone prosthesis, and itstechnical details can be found in many patents, for examples U.S. Pat.Nos. 4,959,104; 5,092,888; 5,180,426; 5,262,166; 5,336,264; 5,525,148;5,053,212; 5,149,368; 5,342,441; 5,503,164; 5,542,973; 5,545,254;5,695,729 and 5,814,681. In general, the prior art calcium phosphatecements suffer one or more drawbacks as follows: 1) additives having arelatively poor bioactivity being required; 2) a complicated preparationprocess; 3) an undesired setting time or working time of CPC, which aredifficult to be adjusted; 4) not capable of being set to a desired shapein water, blood or body fluid; and 5) poor initial strength aftersetting of the CPC.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a calcium phosphatecement.

Another object of the present invention is to provide a calciumphosphate cement comprising particles having whiskers or fine crystalson surfaces of the particles. Still another object of the presentinvention is to provide a process for preparing a calcium phosphatecement.

A further object of the present invention is to provide a method oftreating a bone or a tooth having a defect in a patient by using acalcium phosphate cement.

In order to accomplish the above objects of the present invention acalcium phosphate cement prepared in accordance with the presentinvention comprises calcium phosphate particles having a diameter of0.05 to 100 microns, wherein said calcium phosphate particles on theirsurfaces have whiskers or fine crystals having a width ranging from 1 to100 nm and a length ranging from 1 to 1000 nm. By adjusting the diameterof the calcium phosphate particles, the width and/or the length of thewhiskers or fine crystals, the inventors of the present invention areable to adjust the working time and/or the setting time of the calciumphosphate cement of the present invention to conform to requirements forvarious purposes. Moreover, the calcium phosphate cement of the presentinvention is fast-setting, and is non-dispersive in water or an aqueoussolution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a normalized particle amount (%) versus particle diameter (pm)plot showing a particle diameter distribution of a calcium phosphatecement (CPC) prepared in accordance with the following Example 6 of thepresent invention.

FIG. 2 is a scanning electron microscopy (SEM) micrograph of the calciumphosphate cement prepared in accordance with Example 6 of the presentinvention.

FIGS. 3 and 4 show the distributions of the lengths and the widths ofthe whiskers or fine crystals on surfaces of the calcium phosphateparticles prepared in the following Example 6 of the present invention,respectively, which are determined directly from transmission electronmicroscopy (TEM).

FIGS. 5 a to 5 c are photographs showing a conventional CPC pasteinjected into water via a syringe at 3, 10 and 30 seconds after theconventional CPC paste being formed.

FIGS. 6 a to 6 c are photographs showing a CPC paste of the presentinvention injected into water via a syringe at 3, 10 and 30 secondsafter the CPC paste being formed in accordance with the followingExample 7.

FIGS. 7 a to 7 c are photographs showing two cylinders prepared byseparately molding a conventional CPC paste and a CPC paste of thepresent invention prepared in the following Example 7, which were takenat 5, 20 and 60 seconds after the two cylinders being immersed in thewater.

FIG. 8 is a TEM micrograph showing the calcium phosphate cement of thepresent invention prepared in the following Example 7.

FIG. 9 is a TEM micrograph showing the calcium phosphate cement of thepresent invention prepared in the following Example 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A suitable process for preparing the calcium phosphate cement of thepresent invention comprises mixing a calcium phosphate powder or smallpieces of calcium phosphate with a wetting agent, and controlling growthof whiskers or fine crystals on surfaces of said calcium phosphatepowder or small pieces of calcium phosphate by an controlling treatment.

Suitable calcium phosphates for use as the calcium phosphate powder orsmall pieces of calcium phosphate in the present invention can be anyknown calcium phosphates such as calcium dihydrogen phosphate,tetracalcium phosphate, calcium dihydrogen phosphate hydrate, acidcalcium pyrophosphate, anhydrous calcium hydrogen phosphate, calciumhydrogen phosphate hydrate, calcium pyrophosphate, calcium triphosphate,calcium polyphosphate, calcium metaphosphate, anhydrous tricalciumphosphate, tricalcium phosphate hydrate, apatite, hydroxyapatite, amixture thereof and an adduct thereof. Moreover, the shape of thecalcium phosphate powder and the shape of the small pieces of calciumphosphate are not limited, which can be spherical or irregular; and thecrystal structure thereof can be single crystal, polycrystal, mixedcrystals, semi-crystal, or amorphous.

The process for preparing the calcium phosphate cement preferablyfurther comprises grinding the resulting product from the controllingtreatment to form calcium phosphate particles having a diameter of 0.05to 100 microns, wherein said whiskers or fine crystals have a widthranging from 1 to 100 nm and a length ranging from 1 to 1000 nm.

Said controlling treatment is a vacuuming treatment, an organic solventtreatment, a microwave treatment, a heating treatment, or any othertreatments which can control growth of whiskers or fine crystals onsurfaces of said calcium phosphate powder or small pieces of calciumphosphate.

Said wetting agent is used to wet the calcium phosphate powder or smallpieces of calcium phosphate, and preferably is a diluted aqueoussolution containing phosphoric acid or phosphate. The amount of saidwetting agent mixed with the calcium phosphate powder or small pieces ofcalcium phosphate, in general, should be enough to wet substantially allthe calcium phosphate powder or small pieces of calcium phosphate.However, it is not necessarily the case when said controlling treatmentis the organic solvent treatment, where a water miscible organic.solvent is added to the mixture of said wetting agent and said calciumphosphate powder or small pieces of calcium phosphate to form a pastefor a subsequent processing step.

Preferably, said wetting agent is a diluted aqueous solution containingmore than 20 ppm of phosphoric acid or phosphate, more preferably morethan 50 ppm, and most preferably more than 100 ppm of phosphoric acid orphosphate.

Preferably, the process for preparing the calcium phosphate cement ofthe present invention comprises soaking said calcium phosphate powder orsaid small pieces of calcium phosphate with said diluted aqueoussolution containing more than 100 ppm of phosphoric acid or phosphate,and carrying out (a) said heating treatment comprising drying theresulting soaked calcium phosphate powder or soaked small pieces ofcalcium phosphate at a temperature higher than 45° C.; (b) saidvacuuming treatment comprising drying the resulting soaked calciumphosphate powder or soaked small pieces of calcium phosphate undervacuum; or (c) said microwave treatment comprising drying the resultingsoaked calcium phosphate powder or soaked small pieces of calciumphosphate by microwave heating. More preferably, the resulting soakedcalcium phosphate powder or soaked small pieces of calcium phosphate iswell mixed to form a uniform mixture prior to being subjected totreatment (a), (b) or (c).

Alternatively, the process for preparing the calcium phosphate cement ofthe present invention comprises mixing said calcium phosphate powder orsaid small pieces of calcium phosphate with said diluted aqueoussolution containing more than 100 ppm of phosphoric acid or phosphate,and carrying out said organic solvent treatment comprising mixing themixture of said wetting agent and said calcium phosphate powder or smallpieces of calcium phosphate with a water miscible organic solvent, anddrying the resulting mixture under vacuum. Preferably, said organicsolvent treatment is carried out while stirring, and more preferably,the mixture of said diluted aqueous solution containing more than 100ppm of phosphoric acid or phosphate and said calcium phosphate powder orsmall pieces of calcium phosphate is well mixed prior to being subjectedto said organic solvent treatment.

Preferably, said calcium phosphate particles of the calcium phosphatecement of the present invention have a diameter of 0.2 to 80 microns,and more preferably 0.5 to 50 microns.

The width of a whisker means an average value of lateral cross-sectionaldiameters of the whisker, and the width of a fine crystal means anaverage value of the first 30% of the diameters of the fine crystal,which are shorter than the other 70% thereof. The length of a finecrystal means an average value of the last 30% of the diameters of thefine crystal, which are longer than the other 70% thereof.

Preferably, said whiskers or fine crystals have a width ranging from 2to 70 nm and a length ranging from 5 to 800 nm, and more preferably alength ranging from 10 to 700 nm.

Preferably, said calcium phosphate particles have a molar ratio ofcalcium to phosphate ranging from 0.5 to 2.5, more preferably 0.8 to2.3, and most preferably 1.0 to 2.2.

The calcium phosphate cement of the present invention is biocompatibleand a paste made therefrom is non-dispersive in water, which has aworking time from several minutes to hours and a setting time from a fewminutes to hours. Consequently, the calcium phosphate cement of thepresent invention is extremely suitable for use as an implant or fillingmaterial in dental or bone prosthesis, where the paste must contactwater, blood or body fluid. Particularly, the paste made from thecalcium phosphate cement of the present invention is able to be directlyinjected into a bone defect or cavity as an implant or filling material.

The present invention also discloses a method of treating a born or atooth having a defect in a patient, comprising mixing the calciumphosphate cement of the present invention and ahardening-promoter-containing aqueous solution to form a paste, and a)injecting said paste into a bone defect or cavity of said patient or b)shaping said paste and implanting the resulting shaped paste into a bonedefect or cavity of said patient.

In the method of the present invention, said calcium phosphate cementmay further comprise a growth factor, a bone morphology protein or apharmaceutical carrier, or said hardening-promoter-containing aqueoussolution further comprises a growth factor, a bone morphology protein ora pharmaceutical carrier.

Said hardening-promoter-containing aqueous solution can be an aqueoussolution comprising any known compounds or compositions which enable thesolidification of calcium phosphate, for examples phosphates, calciumsalts, and fluorides. That is said hardening-promoter-containing aqueoussolution may be an aqueous solution comprising phosphate ions, calciumions, fluorine ions, or phosphate ions together with fluorine ions as ahardening promoter.

The content of said hardening promoter in saidhardening-promoter-containing aqueous solution has no speciallimitation, but preferably ranges from 1 mM to 3 M, and more preferablyfrom 10 mM to 1 M.

The mixing ratio of the calcium phosphate cement of the presentinvention and said hardening-promoter-containing aqueous solution is notrestricted to any particular ranges; however, the amount of saidhardening-promoter-containing aqueous solution mixed should besufficient to provide substantial wetting of the calcium phosphatecement of the present invention. It should be noted that more water canbe supplied in-situ from saliva or body fluid, when the paste isinjected or implanted into the bone defect or cavity. Further, thecontent of said hardening promoter in said hardening-promoter-containingaqueous solution should be adjusted to a higher level corresponding to aless amount of said hardening-promoter-containing aqueous solution beingmixed.

EXAMPLE 1

Heating Treatment

5 g of Ca(H₂PO₄)₂ . H₂O powder and 1.6 ml of 25 mM phosphoric acidaqueous solution were mixed, and stirred for one minute. The resultingmixture was placed into an oven at 50° C. for 15 minutes, and theresulting dried mixture was mechanically ground for 20 minutes to fineparticles after being removed from the oven. 1 g of the fine particlesand 0.4 ml of phosphate aqueous solution (1.0 M, pH=6.0) were mixed toform a paste, which was tested every 30 seconds to determine the workingtime and the setting time. The setting time is the time required when a1 mm diameter pin with a load of ¼ pounds can be inserted only 1 mm deepinto the surface of the paste. The working time is the time after whichthe paste is too viscous to be stirred. The working time of the paste ofthis example is 30 minutes and the setting time thereof is one hour.

The paste was placed in a relatively large amount of deionized waterimmediately following the formation thereof, and it was observed thatthe paste was non-dispersive in deionized water.

EXAMPLE 2

Vacuuming Treatment

5 g of CaHPO₄ (DCPA) powder and 1.2 ml of 25 mM phosphoric acid aqueoussolution were mixed, and stirred for one minute. The resulting mixturewas placed in a vacuum environment of −100 Pa for 30 minutes, and theresulting dried mixture was mechanically ground for 20 minutes to fineparticles. 1 g of the fine particles and 0.4 ml of phosphate aqueoussolution (1.0 M, pH=6.0) were mixed to form a paste, which was testedevery 30 seconds to determine the working time and the setting time. Theworking time of the paste of this example is 20.5 minutes and thesetting time thereof is 24 minutes.

The paste was placed in a relatively large amount of deionized waterimmediately following the formation thereof, and it was observed thatthe paste was non-dispersive in deionized water.

EXAMPLE 3

Organic Solvent Treatment

5 g of CaHPO₄ (DCPA) powder and 1.6 ml of 25 mM phosphoric acid aqueoussolution were mixed, and stirred for one minute. To the resultingmixture 1.6 ml of acetone was added while stirring to form a pastefollowed by placing in a vacuum environment of −100 Pa for one hour, andthe resulting dried mixture was mechanically ground for 20 minutes tofine particles. 1 g of the fine particles and 0.4 ml of phosphateaqueous solution (1.0 M, pH=6.0) were mixed to form a paste, which wastested every 30 seconds to determine the working time and the settingtime. The working time of the paste of this example is 20.0 minutes andthe setting time thereof is 22.0 minutes.

The paste was placed in a relatively large amount of deionized waterimmediately following the formation thereof, and it was observed thatthe paste was non-dispersive in deionized water.

EXAMPLE 4

Microwave Treatment

3 g of a mixed powder of CaHPO₄ (DCPA) and Ca₄(PO₄)₂O (TTCP) in 1:1molar ratio was mixed with 2.0 ml of 25 mM phosphoric acid aqueoussolution, and the mixture was stirred for five minutes. The resultingmixture was placed in a microwave oven where it was heated under lowpower for five minutes. The resulting dried mixture was mechanicallyground for 20 minutes to fine particles. 1 g of the fine particles and0.42 ml of phosphate aqueous solution (1.0 M, pH=6.0) were mixed to forma paste, which was tested every 30 seconds to determine the working timeand the setting time. The working time of the paste of this example is2.0 minutes and the setting time thereof is 4.0 minutes.

The paste was placed in a relatively large amount of deionized waterimmediately following the formation thereof, and it was observed thatthe paste was non-dispersive in deionized water.

EXAMPLE 5

Heating Treatment

5 g of a mixed powder of DCPA and TTCP in 1:1 molar ratio was mixed with1.6 ml of 25 mM phosphoric acid aqueous solution, and the mixture wasstirred for one minute. The resulting mixture was placed in a hightemperature oven at 500° C. for five minutes. The resulting driedmixture was mechanically ground for 20 minutes to fine particles. 1 g ofthe fine particles and 0.4 ml of phosphate aqueous solution (1.0 M,pH=6.0) were mixed to form a paste, which was tested every 30 seconds todetermine the working time and the setting time. The working time of thepaste of this example is 1.5 minutes and the setting time thereof is 2.5minutes.

The paste was placed in a relatively large amount of deionized waterimmediately following the formation thereof, and it was observed thatthe paste was non-dispersive in deionized water.

EXAMPLE 6

Heating Treatment

5 g of a mixed powder of DCPA and TTCP in 1:1 molar ratio was mixed with1.6 ml of 25 mM phosphoric acid aqueous solution, and the mixture wasstirred for one minute. The resulting mixture was placed in a hightemperature oven at 1000° C. for one minute. The resulting dried mixturewas mechanically ground for 20 minutes to fine particles. 1 g of thefine particles and 0.4 ml of phosphate aqueous solution (1.0 M, pH=6.0)were mixed to form a paste, which was tested every 30 seconds todetermine the working time and the setting time. The working time of thepaste of this example is 31 minutes and the setting time thereof is 35minutes.

EXAMPLES 7-11

The procedures of Example 1 were repeated except that the Ca(H₂PO₄)₂ .H₂O powder was replaced by a mixed powder of DCPA and TTCP in 1:1 molarratio and the 25 mM phosphoric acid aqueous solution was replaced by adiluted phosphoric acid aqueous solution having a pH of 1.96. Theheating treatments were carried out with conditions listed in Table 1.The performance is also listed in Table 1.

CONTROL EXAMPLE 1

1 g of a mixed powder of DCPA and TTCP in 1:1 mole and 0.4 ml of adiluted phosphoric acid aqueous solution having a pH of 1.96 were mixedto form a paste, which was tested every 30 seconds to determine theworking time and the setting time. The paste of this example can not setwithin hours. The performance is listed in Table 1.

EXAMPLE 12

The procedures of Example 2 were repeated except that the DCPA powderwas replaced by a mixed powder of DCPA and TTCP in 1:1 molar ratio andthe 25 mM phosphoric acid aqueous solution was replaced by a dilutedphosphoric acid aqueous solution having a pH of 1.96. The performance islisted in Table 1.

EXAMPLE 13

The procedures of Example 3 were repeated except that the DCPA powderwas replaced by a mixed powder of DCPA and TTCP in 1:1 molar ratio andthe 25 mM phosphoric acid aqueous solution was replaced by a dilutedphosphoric acid aqueous solution having a pH of 1.96. The performance islisted in Table 1.

EXAMPLE 14

The procedures of Example 4 were repeated except that the 25 mMphosphoric acid aqueous solution was replaced by a diluted phosphoricacid aqueous solution having a pH of 1.96. The performance is listed inTable 1.

TABLE 1 Setting/working Dispersive Controlling treatment time (min) inWater Control Ex. 1 — — Yes Ex. 7 Heating, 50° C. 11.5/6.5  No Ex. 8Heating, 100° C. 13.5/8.0  No Ex. 9 Heating, 150° C. 8.5/8.0 No Ex. 10Heating, 500° C. 2.5/1.5 No Ex. 11 Heating, 1000° C. 35/31 No Ex. 12Vacuuming 14.5/11.5 No Ex. 13 Organic solvent 17.5/16.5 No Ex. 14Microwave 3.5/2.5 No

The pastes prepared in Control Example 1 and Example 7 were injectedinto water via a syringe at 3, 10 and 30 seconds after the paste beingformed. The results are shown in FIGS. 5 a to 5 c and FIGS. 6 a to 6 c,respectively. It can be seen from FIGS. 5 a to 5 b that the pasteprepared in Control Example 1 is dispersive in water. On the contrary,the paste prepared in Example 7 is non-dispersive as shown in FIGS. 6 ato 6 c.

Two cylinders were prepared by separately molding the pastes prepared inControl Example 1 and Example 7, and were then placed in water. FIGS. 7a to 7 c show the pictures taken at 5, 20 and 60 seconds after thecylinders being immersed in the water, from which it can be seen thatthe left cylinder made from the paste prepared in Control Example 1collapses, while the right cylinder made form the paste prepared inExample 7 remains almost intact.

It can be concluded from the results shown in FIGS. 5 a to 7 c that thepaste prepared from the calcium phosphate cement of the presentinvention can be directly injected or implanted after being molded intoa block into a cavity in a deformed tooth or bone.

Two samples of the calcium phosphate cement prepared in Example 7 wereobserved by transmission electron microscopy (TEM), and the two TEMpictures shown in FIGS. 8 and 9 indicate that there are whiskers onsurfaces of calcium phosphate particles having different diameters ofthe calcium phosphate cement.

The calcium phosphate cement prepared in Example 6 has a particlediameter distribution shown in FIG. 1, which was determined by usingparticle size analyzer (Sald-2001, Shimadzu Co., Japan). The curve inFIG. 1 indicates that the particle diameters of the calcium phosphatecement prepared in Example 6 range from about 0.47 microns to 93.49microns. FIG. 2 shows a scanning electron microscopy (SEM) micrograph ofthe calcium phosphate cement prepared in Example 6. Moreover, thelengths and the widths of the whiskers or fine crystals on surfaces ofthe calcium phosphate particles prepared in Example 6 were determineddirectly from TEM (JXA-840, JEOL Co., Japan), and the results are shownin FIGS. 3 and 4, respectively. As shown in FIGS. 3 and 4, the lengthsand widths of the of the whiskers or fine crystals on surfaces of thecalcium phosphate particles prepared in Example 6 range from 1 to 625 nmand 1 to 65 nm, respectively.

EXAMPLES 15-19

The procedures of Example 7 were repeated by using the calcium phosphatepowders and the wetting solutions listed in Table 2. The performance isalso listed in Table 2.

TABLE 2 Calcium phosphate Wetting Heating Setting/working Dispersive inpowder* solution treatment time (min) water Ex. 15 TCP Acetic acid Yes 10/6.5 No Control TCP — No Yes Ex. 2 Ex. 16 TCP Acetic acid Yes12.5/8.5  No Control TCP — No — Yes Ex. 3 Ex. 17 TTCP + DCPA PhosphoricYes 11/18 No acid Control TTCP + DCPA — No — Yes Ex. 4 Ex. 18 TTCP +DCPA + TCP Phosphoric Yes — No acid Control TTCP + DCPA + TCP — No — YesEx. 5 Ex. 19 DCPA + TCP Phosphoric Yes 29/24 No acid Control DCPA + TCP— No — Yes Ex. 6 *TCP is anhydrous tricalcium phosphate. TTCP + DCPA isa mixed powder of TTCP and DCPA in 1:1 molar ratio. TTCP + DCPA + TCP isa mixed powder of TTCP + DCPA and TCP in 1:1 weight ratio. DCPA + TCP isa mixed powder of DCPA and TCP in 1:2 molar ratio. DCPA + TCP is a mixedpowder of DCPA and TCP in 1:2 molar ratio.

CONTROL EXAMPLES 2-6

The procedures of Control Example 1 were repeated by using the calciumphosphate powders and the wetting solutions listed in Table 2. Theperformance is also listed in Table 2.

EXAMPLES 20-31

The procedures of Example 7 were repeated by using the wetting solutionshaving different pH values listed in Table 3. The performance is alsolisted in Table 3.

CONTROL EXAMPLES 7-14

The procedures of Control Example 1 were repeated by using the wettingsolutions having different pH values listed in Table 3. The performanceis also listed in Table 3.

TABLE 3 Heating Dispersive Wetting solution pH treatment in water Ex. 20Phosphoric acid 0.56 Yes No Control Ex. 7 — — No Yes Ex. 21 Phosphoricacid 1.03 Yes No Ex. 22 Phosphoric acid 1.17 Yes No Ex. 23 Phosphoricacid 1.22 Yes No Ex. 24 Phosphoric acid 1.32 Yes No Ex. 25 Phosphoricacid 2.0  Yes No Control Ex. 8 — — No Yes Ex. 26 Acetic acid + sodium7.0  Yes No carbonate Control Ex. 9 — — No Yes Ex. 27 Sodium hydroxide9.5  Yes No Control Ex. 10 — — No Yes Ex. 28 Sodium hydroxide 12.55  YesNo Control Ex. 11 — — No Yes Ex. 29 Acetic acid 1.96 Yes No Control Ex.12 — — No Yes Ex. 30 Ethanol — Yes No Control Ex. 13 — — No Yes Ex. 31Deionized water 7.0  Yes No Control Ex. 14 — — No Yes

1. A method of forming calcium phosphate cement particles with calciumphosphate crystals on the surface of the particles comprising: forming amixture by contacting calcium phosphate particles with an acidic wettingagent, wherein the calcium phosphate particles comprise tetracalciumphosphate and dicalcium phosphate anhydrous; subjecting the mixture toone or more controlling treatments, wherein at least one of thecontrolling treatments substantially removes the wetting solution fromthe mixture, and wherein the controlling treatment is chosen such thatthe treatment causes the growth of fine crystals or whiskers on thesurface of at least a portion of the calcium phosphate particles; andreducing the size of the calcium phosphate particles such that thecalcium phosphate particles have an average diameter ranging from 0.05microns to 100 microns.
 2. The method of claim 1, wherein the calciumphosphate particles are contacted with the wetting agent for 1 minute to5 minutes.
 3. The method of claim 1, wherein the wetting agent is anaqueous phosphoric acid solution.
 4. The method of claim 1, wherein thewetting agent is acetic acid.
 5. The method of claim 1, wherein thewhiskers have a length ranging from 10 microns to 700 nm.
 6. The methodof claim 1, wherein the at least one controlling treatment is avacuuming treatment.
 7. The method of claim 1, wherein the controllingtreatment is selected from the list consisting of a vacuuming treatment,a heating treatment, a microwave treatment and an organic solventtreatment.
 8. The method of claim 7, wherein the controlling treatmentis an organic solvent treatment.
 9. The method of claim 7, wherein thecontrolling treatment is a microwave treatment.
 10. The method of claim7, wherein the controlling treatment is a heating treatment.
 11. Themethod of claim 10, wherein the mixture is heated to a temperature ofgreater than 45° C.